Electric heating apparatus



Maich 7, 1933. E. D. MCARTHUR, 1,900,573

I ELECTRIC HEATING APPARATUS Filed Nov. 19, 19:50

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Inventor-z Tim-war D. McAr'thur,

His Attorney.

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a uuubn filcdlovelber 19, mo. Serial Re. 40am.

7 My invention relates to electric heatingapparatus, more particularly to electric heaters of the'type in which the-heat is nerated in the heated body itself. and has or its object simple, reliable and efi'ective electric heating apparatus utilizing currents of high frequenc1es.

Myinvention has particular application to heating apparatus wherein the material or efictrtlildfes electrically lconnlecteiilJ tohabsoalrce o ig requency'supp y w ere yt e o y1s heated by an electrostatic field. In the application of this t found that the portion of the body adjacent the source of high frequency supply is heated with greater rapidity than the remaining more remotely situated Iportion. In accordance with my invention rovide in one form thereof a series of pairs 0 heating electrodes 1 with separate source of high frequency supply which are arranged on opposite sides of I the pairs of plates, together*with=means for assmgthe' dy to be heated in succession etween the pairs of plates whereby it is heated uniformly. My'invention is especially useful in the heating of food products, such as milk and meat, for sterilization, cooking or other purposes. It has wide application, however, to eating processes-wherein aluniform rate of heating is desirable. This method of heating is to be distinguished from the usual method of heating in which heat is ap lied to the ex-' terior ofthe hody-and-must e transmitted by conduction into the interior portions. Such methodsrequire a longer heating period and furthermore, the outer portions of the a body are subjected to the maximum temperainterior portions. which is of especial disadvantage where the heating period is quite critical and must be closely controlled.

For a more complete understanding of my invention reference should be had to the accompanying drawing in which Fig. 1 is a view showing in simplified partially diagrammatic form apparatus forapplying high frequency current to the heating plates in accordance m with my invention, while Fig. 2 is a diagrambody to be heated is placed between spacede of heater it has been ture for a greater length of time than the matic representation of heating apparatus to be heated is placed between the plates in s seed or electrically insulated relation with t em, for example in a suitable container 13 made of an electrically insulating material,

such. as glass. s

It will be understood'that the electron dis" charge device 12 operates in a manner similar to a high frequency short wave tube oscillator,

such as used in radio transmission, and produces currentof similar high frequencies, on

the order of twenty to fifty million cycles per second. In the particular system shown the plates 10 and 11 are connected respectively to the grid 14 and the anode or plate 15 of the discharge device, suitable inductances 16 I and 16a being included in the respective connections so as to form a resonant high frequency oscillation circuit. At these very high requencies the inductance in the conductors 3 themselves may be suflicient to reduce this desired resonant condition in w ich case no auxiliary inductance would be provided.

. The filamentary cathode 17 of the discharge device is heated from a-suitable source of alternating current which is connected to thecathode through a suitable transformer 18. Radio frequency coils 19 and 20 are included in the sides respectively of the cathode circuit. A tap 21 on the secondary of the transformer 18 leads through a-irrid leak resistance 22 and capacity 23 connected in parallelwith each other, and. through a choke coil 24 to the grid 14. A suitablesource of electrical supply, for example a direct current source of 500 volts or more, is connected to the to 21 and the plate 15, a radio frequency cho e coil 25 being included in the connection with the plate; The 'positive side Q It is very effective in the heating of various of the supplysource is connected to the plate and the negative side to tap 21.

It will be understood that the frequency generated in the oscillation circuit including the two plates may be varied by changing the constants of the circuit, for example by varying the distance between the two plates liquids, and materials containing moisture, such as articles of food including meats, vegetables, eggs, milk, etc, when for some reason it is undesirable to apply heat externally as from an hot oil bath or an oven.

It'mayalso be used in drying laundry.

In the use of the heating a paratus for some materials I have found t at the electrode of each pair which is nearer the source of, high frequency supply apparently has the greater heatingefiect, the portion of the material adjacent this electrode being heated more rapidly than the remaining portions.

In the arrangement shown, the material ad-.

jacent the plate 10 is heated most rapidly. One explanation of this is the distortion of theelectrostatic field due to the difference in the lengths of the conductors leading from the two lates to the source of'supply. The plate 10 in nearer the source of high freuency'suplp y constituted by the discharge evice 12 a the lead to the other plate 'mustpass the first plate and distorts the field due to its prox- 1m1y.' p

Asshown in Fig. 2,1provide in accordance with one'form of my invention a plurality of pairsof plates'26 to '29 inclusive which are mounted preferablyin e ually spaced relation and with corresponding plates in alignment, together with suitable conveying means, such as a continuous conveyor 30 passing successively between the pairs of plates. The sources of high frequency supply 31 to 34 inclusive for the respectivepairs of plates are placed on alternate opposite sides of the conveyor. It will be'understood that the sources 31 and 34 are suitable sources of high frequency current, such as shown i Fig. 1, there being a separatesource con nected to. each pair of plates." The material to be heated is passed on the conveyor in the containers-13 successively between the 'opgosite sides to the higher rate of heating s the shorter lead and cons'e- 'quently gives the greater heating efi'ect since pairs of plates and consequently the material in each container is subjected alternately on as a result the material is heated uniformly throughout. It will be understood that the number of airs of heating plates may be varied as desired to give the desired temperature and rate of heatingl While I have shown a particular embodi ment' of my-invention, it will be understood, of course, that I do not wish to be limited thereto since many modifications may be made, and I, therefore, contemplate by, the appended claims to cover any such modifications as fall within the true spirit and scope of my invention.

What I claim as new and desire to protect by Letters Patent of the United States is:

1. Electric heating apparatus comprising a plurality of pairs of electrodes, aseparate source of high frequency supply for each of said pairs of electrodes, one of the electrodes of each pair giving a greater heating e'liect than the other and means forpassmg the material to be heated between said pairs of electrodes in succession in such manner that different ortions of said materialare adjacent the e ectrode givingthe greater heating efiect whereby said material is heated uniformly.' Y

2. Electric heatingap aratus comprisinga plurality of airs ofe ectrodes, a se arate source of big frequency current su p y for each of said pairs of electrodes, the'e ectrodesof each pair' being respectively closely and remotely situated with respect toth'eir supply source, and means for passing the material to be heated between the electrodes of a said pairs in succession in such manner that a given portion of the'materlal is alternately adjacent said closely and remotely situated electrodes. v

3. Electric heating up aratus comprisin a plurality of pairs of'e ectrodes, means or electrodes of said pairs in succession, a source of high frequenc current for each of said pairs of electro es', said sources being .arranged on opposite sides of the path of travel of said material in such a manner that each of said sources is res ectively closely and remotely situated wit res set to its electrodes whereby a predetermine portion of saidmaterial passes adjacent the electrodes giving difierent rates of heating.

In witness whereof I ave hereunto set my hand this 18th day of November,1930. v ELMER D. MQARTHUR.

passing the material to be heated between the r 

